The invention relates generally to the reproduction of a master or original.
More particularly, the invention relates to the production of correctly oriented copies of a transparent master, especially a diapositive which is framed without glass, using a procedure in which the master is photoelectrically scanned point-by-point and line-by-line. The printing or imaging signals generated during scanning are entered in a memory. The image represented by the printing signals is subsequently printed on light-sensitive copy material point-by-point and line-by-line in that the signals are read out from the memory and used to control a printing beam.
A difficulty exists in the production of copies of a framed diapositive. This difficulty stems from the fact that the marks at the margins of the diapositive are covered by the frame and are thus not available to determine whether the diapositive is properly oriented on the copying platform. As a rule, and particularly when so-called service frames are involved, the two sides of the frame of a diapositive are differently colored. One side is white and the frame is positioned so that such side faces the light source which is used to transilluminate the diapositive and project an image of the same onto the copy material. On the one hand, this reduces heating of the frame. On the other hand, for the purpose of placing the framed diapositive on the copying platform of a copying apparatus, it can be assumed that the emulsion is located on the side of the frame which faces away from the white side.
However, in addition to diapositives in service frames, there are diapositives which have been framed by amateurs fond of photographs. Furthermore, for reasons which are not always clear, diapositives are sometimes removed from a service frame and then improperly replaced because of a lack of knowledge of the proper orientation. Diapositives which are placed on the platform in a inverted position naturally result in inverted copies.
The patent literature discloses methods which make it possible to detect the emulsion by machine even when a diapositive is framed without glass. See, for example, the German Offenlegungsschrift 36 35 386. The method described here is based on the fact that, when a directed light beam impinges upon the emulsion of a developed photographic film, the reflected beam contains a higher proportion of scattered light than a beam reflected from the opposite side of the film. When a framed diapositive lying on the copying platform is found to be improperly oriented using this method, the diapositive must be removed, rotated and once again placed on the platform. This causes a considerable delay in the copying procedure.
Another method for detecting the position of the emulsion is described the German Offenlegungsschrift No. 40 31 108 of the present assignee. Here, the coarseness of one side of a film is determined by means of a sensing head and compared with the coarseness of the other side. This makes it possible to immediately ascertain when the emulsion faces in the wrong direction. However, there is again the problem of bringing an improperly oriented film into the correct position without a substantial loss of time.